HVAC Filter MERV ratings - which is best (for my usage)?

June 12, 2009 12:09 PM

HVACFilterfilter: It's time to get a new filter for my residential HVAC system. Please help me understand MERV ratings.

I've done quite a bit of research and it appears to me that MERV rated filters up to about 6 or so are used mostly to keep the insides of the HVAC unit itself clean & operational and that filters rated 7-12 are used for further conditioning the air itself. I.E. - filtering out dust/dander particles to prevent them from being breathed in & keeping the house cleaner as well. Is this assumption correct? In theory I can see it, does real world experience bear this out?

My house is a small 1000sf open plan with one bedroom that stays mostly closed off & a small bathroom that mainly stays open. I live with a flock of 9 parrots, three of which are old world birds who produce a *lot* of dander. Will the higher MERV rated filters help with the dander/powder? Or should I just keep dusting regularly & get the lower MERV (and substantially cheaper) rated filter? I'll note the air return is right next to the front door and away from most all activity in the house.

The filters themselves range anywhere from $8USD x 12 (MERV 6) to $16USD x 6 (MERV 12) when bought in bulk. They're generally $15 - $50 when sourced individually. I'm concerned that not only are the higher rated filters substantially more expensive, it appears they require a more rigid rotation schedule and could possibly bind up or air lock my HVAC system. I'm using a 20x20x4 filter which should get between 3 (Merv 12) & 6 or more (Merv 6) months per filter - which makes it look like the higher rated units are at least four times as expensive. The one that came with the unit when it was new a little over a year ago was touted as "change every year or two" by my HVAC guy - I took it out and banged a lot of the powder off it before firing up the A/C for the summer today & it seems to be working fine. I don't want to push it, though. I called my HVAC subcontractor and they didn't have a clue. So, here I am, trying to figure this out before dropping a huge chunk of change on a bulk purchase of filters I'll be using for the next few years. TIA!

posted by torquemaniac to home & garden (3 comments total)

I can speak to this somewhat, as I have five cockatiels. However, living in Arizona, generally when I have to run the AC it runs so much I have to change the filters every 4-6 weeks so I've never tried the pricier ones. It's really difficult to say if a higher MERV will remove more dander from the air in real world conditions. The higher MERV filters will catch smaller particles, however your HVAC will move less air. Those finer filters allow less air through to start, and clog more quickly. In my opinion you'd be better off buying a dedicated air filtration unit, but that's really just a guess.
posted by TungstenChef at 12:33 PM on June 12

A little googling around indicates that powder down particles are ~1 micron in size. According to this page that means you're going to have to have a MERV 12 to efficiently filter it out.
posted by TungstenChef at 12:49 PM on June 12

Actually, LEED requires that (not that you're meeting LEED requirements), during construction an operating air handling unit should be fitted with a filter with at least a rating of 8 MERV - this is to protect the unit from airborne dust and stuff kicked up by the construction process. Once the building is occupied, the filter needs to be upgraded to 13 MERV, for the comfort and well-being of building occupants. So, your assumption on the purposes of the ratings is pretty much correct. LEED credt requirements are generally substantially more stringent than "standard", though.
posted by LionIndex at 1:38 PM on June 12